1. Field of the Invention
The present invention relates to a method for manufacturing a polymer optical waveguide and particularly to a method for manufacturing an optical component such as an optical integrated circuit, optical interconnection, optical coupler or the like.
2. Description of Related Art
Inorganic materials such as quartz glass, multi-component glass or the like, which are characterized by a low optical transmission loss and a wide transmission band, have been widely used as a base material for optical components or optical fibers. Recently, polymer materials have also been developed and are made attractive as materials for optical waveguides because they are superior in workability and cost to the inorganic materials. For example, proposed is a flat plate type optical waveguide having a core-clad structure where a core is formed of a polymer with an excellent transparency, such as polymethyl methacrylate (PMMA) or polystyrene, and a cladding layer is formed of a polymer having a refractive index lower than that of the core material (Japanese Unexamined Patent Publication JP-A 3-188402 (1991)).
On the other hand, a flat plate type optical waveguide with lower loss has been realized by Matsuura et al. using a polyimide which is a transparent polymer of high thermal resistance Japanese Unexamined Patent Publication JP-A 4-9807 (1992)).
These methods, however, need core pattern formation with a photoresist and subsequent recess and projection formation by reactive ion etching or the like for every plate in order to form a core structure on the surface of a cladding layer, and accordingly present problems in mass productivity and price-lowering. Therefore, attempts have been conducted for enhancing the mass-productivity of optical waveguides by performing the injection molding with a mold having a surface processed to have a recess and projection corresponding to a core pattern of the wave guide. In this injection molding, only materials of low glass transition temperature can be used.
An object of the invention is to provide a method for manufacturing an optical waveguide using a mold for reproducing a core profile to attain costless and simple mass-production of a polymer optical waveguide with low loss and high reliability. In order to achieve such object, it is important that polymer films of various thicknesses are completely stripped from the mold without remaining foreign matters.
The invention provides method for manufacturing a polymer optical waveguide comprising at least a cladding layer of a first polymer, and a core portion of a second polymer formed in a recessed portion provided on a surface of the cladding layer of the first polymer, the method comprising the steps of:
coating the first polymer in molten state or in solution to a molding plate having a projected shape in cross section for forming the core portion, curing the first polymer by ultraviolet rays or by heat, and then stripping the cured first polymer from the molding plate, thereby obtaining the cladding layer having the recessed portion transferred to the surface thereof from the molding plate.
According to the invention, (1) since material of high thermal resistance, use of which is difficult in the injection molding, can be used, a thermal resistance required in soldering for mounting electronic components or the like on an obtained optical waveguide substrate can be achieved. (2) Since the first polymer of lower viscosity can be used for transfer, a high fidelity transfer having a transfer rate of approximately 100% can be achieved. (3)An optical waveguide substrate can be molded in the form of a film. (4) A multi-mode optical waveguide such as one having a core height of 50 xcexcm and capable of being molded with high aspect ratio can easily be realized.
In addition, while some consideration has been required in conventional injection molding for controlling temperature in the mold to be unified, it is easy in the invention to unify the heating or light irradiation for curing the resin.
The invention also provides a method for manufacturing a polymer optical waveguide comprising at least a cladding layer of a first polymer, and a core portion of a second polymer formed in a recessed portion provided on a surface of the cladding layer of the first polymer, the method comprising the steps of:
coating the second polymer in molten state or in solution to a molding plate having a recessed shape in cross section for forming the core portion, curing the second polymer by ultraviolet rays or by heat, thereto applying the first polymer in molten state or in solution, and after curing, stripping the cured first and second polymers from the molding plate.
According to the invention, (1) since material of high thermal resistance, use of which is difficult in the injection molding, can be used, a thermal resistance squired in soldering for mounting electronic components or the like on an obtained optical waveguide substrate can be achieved. (2) Since the first polymer of lower viscosity can be used for transfer, a high fidelity transfer having a transfer rate of approximately 100% can be achieved. (3) An optical waveguide substrate can be molded in the form of a film. (4) A multi-mode optical waveguide such as one having a core height of 50 xcexcm and capable of being molded with high aspect ratio can easily be realized.
In addition, while some consideration has been required in conventional injection molding for controlling temperature in the mold to be unified, it is easy in the invention to unify the heating or light irradiation for curing the resin.
In the invention it is preferable that the first or second polymer is coated on the surface of the molding plate after forming a sacrifice layer for facilitating stripping-off of the polymer from the molding plate.
According to the invention, by adjusting the film thickness of the sacrifice layer, the core diameter of the mold can be changed.
While a mold release agent has conventionally been mixed in the polymer resin in order to facilitate the stripping of the polymer resin after molding, according to the invention the mixing of a release agent is not required. Therefore, the polymer resin can be easily stripped without lowering the optical performance of the resin.
In the invention it is preferable that the molding plate and the polymer are exposed to an atmosphere of liquid or vapor when the first polymer or the second polymer is stripped from the molding plate.
While a mold release agent has conventionally been mixed in the polymer resin in order to facilitate the stripping of the polymer resin after molding, according to the invention the mixing of a release agent is rot required. Therefore, the polymer resin can be easily stripped without lowering the optical performance of the resin.
In the invention it is preferable that the sacrifice layer is of a silicon oxide and is removed by etching.
In the invention it is preferable that the molding plate is a silicon wafer and the sacrifice layer is of a silicon oxide obtained by thermally oxidizing the silicon wafer.
In the invention it is preferable that the molding plate is of a polymer resin and the cured polymer is stripped from the molding plate by soaking both in a liquid.
In the invention it is preferable that a second cladding layer of a third polymer is formed on the cladding layer and the core portion.
The methods mentioned above enable easy stripping of a cured polymer from a molding plate and mass-production of polymer optical waveguides of various film thicknesses.
Incidentally, the polymer for forming upper and lower cladding layers and a core preferably has a Tg (glass transition temperature) of 150xc2x0 C., more preferably of 200xc2x0 C., as measured by DSC (differential scanning calorimetry) in an atmosphere of nitrogen at a temperature-raising rate of 10xc2x0 C./min.